For one thing, ASL has certain morphemes that are expressed through use of external objects, facial expressions, etc. Things other than hands.
Another, bigger problem is that ASL is not English. You can't just take a word, translate it into a different language and assume you have a valid sentence in the target language.
There is a very detailed explanation written in this letter [1], by the linguistics department of UW. That is in contrast to the press office of UW. Among other things: [...] Deaf signers who have viewed the demonstration video of SignAloud do not recognize what is being demonstrated as ASL: [...]
Unfortunately (IMHO) this letter[1] got mixed with a lot of politics in it, but the technical aspect is solid.
[1] https://catalyst.uw.edu/workspace/file/download/5c706e255e89...